This invention relates generally to the field of consolidating hard metallic bodies, and also to rapid and efficient and heating and handling of granular media employed in such consolidation, as well as rapid and efficient heating and handling of preform powdered metal or metal bodies to be consolidated, where such bodies consist essentially of functionally gradient materials, designated herein as FGM. Such materials when consolidated exhibit along a body dimension or dimensions decreased or varying strength or ductility (strain hardening).
The technique of employing carbonaceous particulate or grain at high temperature as pressure transmitting media for producing high density metallic objects is discussed at length in U.S. Pat. Nos. 4,140,711, 4,933,140 and 4,539,175, the disclosures of which are incorporated herein, by reference.
The present invention provides improvements in such techniques, and particularly improvement leading to consolidation of bodies consisting essentially of functionally gradient material (FGM) compositions. One example is tantalum or tantalum together with other metals. Such metals, one or more of which may be consolidated with tantalum, include tungsten, copper, hafnium, rhenium, platinum, gold, molybdenum, uranium, titanium, zirconium and aluminum.
It is a major object of the invention to provide for consolidation of metallic powder consisting of selected metals as referred to, and as may be employed in target penetration, drilling, and related impact activities. Such selected metals typically are distributed as FGMs, as referred to.
It is another object of the invention to provide rapid and efficient heating of carbonaceous and/or ceramic particles used as pressure transmitting media, and also transfer of heat generated in the particles to the work, i.e. the hard metal preform to be consolidated. Basic steps of the method of consolidating the preform metallic body in any of initially powdered, sintered, fibrous, sponge, or other form capable of compaction, or densification (to reduce porosity) then include the steps:
a) providing flowable particles having carbonaceous and ceramic composition or compositions,
b) heating the particles to elevated temperature,
c) locating the heated particles in a bed,
d) positioning the preform body at the bed, to receive pressure transmission,
e) effecting pressurization of said bed to cause pressure transmission via said particles to the body, thereby to compact the body into desired shape, as for example cylindrical shape, increasing its density, and
f) the body consisting essentially of one or more metals selected from the following group: tungsten, rhenium, uranium, tantalum, platinum, copper, gold, hafnium, molybdenum, titanium, zirconium and aluminum,
g) the consolidated body having, along a body dimension, one of the following characteristics:
i) decreasing strength
ii) increasing ductility
iii) decreasing strength, and increasing ductility.
Another object is to achieve rapid or almost instantaneous densification of a composite metal alloy system, the resultant material being fine grained, isotropic, and maintaining original metastable microstructures.
A further object is to produce a consolidated functionally gradient material (FGM) for use as a shaped, heavy metal penetrator EFP (explosively formed penetrator) or SCL (shaped charge lines). One highly advantageous and particular FGM material powder system is comprised of a tantalum and other heavy metal powdered alloy outer section, and transitioning to a different density based powder. It may include an intermediate layer of metal matrix composite of the heavy metal alloy, and lower density powder, and a monolithic lower density base section. The powdered material system for process A may typically employ tantalum particles coated with a pre-alloyed binder composition but other elementally blended, mixed or otherwise combined particles are applicable. The total binder may typically consist of elemental metals selected from the group tungsten, copper, tantalum, hafnium, rhenium, platinum, gold, molybdenum, and uranium hereinafter referred to as HMG, of approximately 16 weight percent of the total composition; but other compositions may be employed. The powdered material system for a process B may typically employ transition layers of one metal to the next with the build-up based on requirements.
The ability to fabricate a functionally gradient heavy metal penetrator in one single forging operation has several advantages. The first is the ability to design and engineer a penetrator with specific and predictable dynamic performance criteria. The second advantage is that of reduced manufacturing costs directly related to fewer hot forging steps. Additional cost reductions are realized in the area of raw material usage by eliminating forging trim and scrappage resulting from the use of a powder metallurgy, near net shape forging preform.
By the use of the methodology of the present invention, substantially improved structural articles of manufacture can be made having minimal distortion, as particularly enabled by the use of carbonaceous, or ceramic, or carbonaceous/ceramic particulate in flowable form.
An additional object includes provision of a method for consolidating hard metal and/or ceramic powder, and/or composite material with or without polymeric powder, to form an object, that includes
a) pressing the FGM into a preform, and preheating the preform to elevated temperature,
b) providing flowable pressure transmitting particles and heating said particles, and providing a bed of said flowable and heated pressure transmitting particles,
c) positioning the FGM preform in such relation to the bed that the particles substantially encompass the preform,
d) and pressurizing the bed to compress said particles and cause pressure transmission via the particles to the preform, thereby to consolidate the preform into a desired object shape, having final density.
The preform typically consists of tantalum complex with metals selected from the HGM group as referred to.
An additional object is to provide a body to be consolidated having varying metallic composition along a body dimension. That varying composition may be characterized by a series of zones, extending either axially or radially for example along the article""s axis, each zone having a characteristic composition which differs from that of an adjacent zone or zones. The metal in successive zones may consist of at least consolidated tantalum, and tantalum consolidated together with one or more metals from the HGM group, and also steel, but in varying proportions in successive zones. For a projectile having great penetration capability, a tapered nose zone may consist primarily of tantalum, and successive zones to the rear may contain less and less tantalum and more and more steel.
For a three metal body, the metals being M1, M2 and M3, the weights W1, W2 and W3 per unit volume of the respective metals M1, M2 and M3 are related and selected, to be as follows:
W1 greater than W2 greater than W3
Other objects are to provide consolidated bodies such as tapered shells, and/or cylindrical and tapered bodies, made by the method of the invention, and having functional gradient properties in two dimensions.
The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation, together with further objectives and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purposes of illustration and description only and are not intended as a definition of the limits of the invention.